Injection molding dies and resin molded products

Abstract

To suppress burrs at gate traces on the molded product surface.SOLUTION: The injection mold 10 has a core mold 14 and a cavity mold 12. The core mold 14 and the cavity mold 12 are superimposed on each other, and molten resin is injected into the cavity 13 formed between the core mold 14 and the cavity mold 12 to form a resin molded product. The mold 10 is provided with a pin gate 16 formed in the cavity mold 12 to inject molten resin into the cavity 13, and the opening diameter of the pin gate 16 is larger than the thickness of the cavity 13 at the position of the pin gate 16.SELECTED DRAWING: Figure 1

Description

Technical Field

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[0001] The present invention relates to an injection mold for injection molding and a resin molded product.

Background Art

[0002] Conventionally, an injection molding technique is known as a technique for molding a resin molded product. The injection molding technique melts a resin material and injects and fills molten resin into a molding space (hereinafter also referred to as a "cavity") formed inside an injection mold (hereinafter also simply referred to as a "mold") that has been processed to provide a molten resin flow path or the like in a metal block. After cooling and solidifying, the separable mold members constituting the mold are separated to open the molding space (hereinafter also referred to as "mold opening"), and the resin molded product is molded by taking out the molded product.

[0003] For example, Patent Document 1 discloses an injection mold in which a pin gate, which is an inlet of molten resin into a cavity, is formed as an injection mold.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Generally, when molten resin is injected into a cavity through a pin gate, the molten resin is cooled and solidified by a core mold and a cavity mold. Then, when the cavity mold and the core mold are opened and a tensile force is applied between the solidified resin in the pin gate and the solidified resin in the cavity at the pin gate position, the resin is cut at the boundary between the gate opening (hereinafter also referred to as the "gate opening") and the molded product.

[0006] When resin is cut in this manner, as shown in the gate mark 16 in Figure 1 of Patent Document 1, a protruding burr may be generated at the gate mark (hereinafter also referred to as "gate mark") that indicates the position of the gate on the molded product.

[0007] This invention was made in view of the above-mentioned problems, and aims to suppress the generation of burrs in the gate marks of molded products. [Means for solving the problem]

[0008] An injection molding die according to the first embodiment has a core mold and a cavity mold, and is an injection molding die for molding a resin molded product by overlapping the core mold and the cavity mold and injecting molten resin into the cavity formed between the core mold and the cavity mold, and is provided with a pin gate formed in the cavity mold for injecting molten resin into the cavity, The opening diameter of the pin gate is greater than the thickness of the cavity at the location of the pin gate.

[0009] In the injection molding die of the first embodiment, the opening diameter of the pin gate formed in the cavity mold is greater than the thickness of the cavity formed between the core mold and the cavity mold at the position of the pin gate (hereinafter also referred to as "wall thickness"). Generally, when molten resin is injected into the cavity through the pin gate, the molten resin is cooled and solidified by the core mold and the cavity mold. However, in areas with thin wall thickness, the molten resin cools faster and solidifies faster than in areas with thick wall thickness due to the difference in heat capacity.

[0010] On the other hand, in this embodiment, by making the opening diameter of the pin gate larger than the thickness of the cavity at the pin gate position, the amount of molten resin inside the pin gate can be increased, thereby increasing the heat capacity. As a result, after the injection of the molten resin is completed, when the molten resin upstream of the gate opening is cooled and solidified by the surrounding cavity mold, the solidification speed is suppressed and becomes relatively slow due to its proximity to the heat source.

[0011] In this way, by controlling the difference in solidification speed between the molten resin inside the pin gate and the molten resin inside the cavity at the pin gate position, and by increasing the difference in thermal shrinkage, distortion is concentrated in layers at the boundary between the solidified resin gate opening and the molded product.

[0012] Generally, when the cavity mold and core mold are opened and a tensile force is applied between the solidified resin in the pin gate and the solidified resin in the cavity at the pin gate position, the solidified resin is constricted at the boundary between the gate opening and the molded product. As a result, stress concentrates in this constricted area, and when the stress exceeds the breaking strength of the solidified resin, a partial fracture, or crack, first occurs on the outer circumference of the constricted area, followed by fracture progressing toward the center, and finally leading to complete separation.

[0013] In this embodiment, fracture is induced along the weakened layer due to strain concentration, making it easier and relatively smooth to cut the solidified resin. This suppresses the generation of burrs and other defects at the gate marks on the molded product.

[0014] The injection molding die of the second embodiment is an injection molding die of the first embodiment, wherein the core mold is formed at a position opposite to the pin gate and includes a residual gas discharge section that discharges residual gas in the cavity to the outside of the injection molding die when molten resin is filled into the cavity.

[0015] When the cavity thickness is thin according to the shape specifications of a resin molded product, a higher injection pressure is required when injecting molten resin into the cavity compared to when the cavity thickness is thicker. This can easily lead to increased load on the molding machine, increased flow rate of molten resin, and resulting distortion of the molded product.

[0016] Therefore, in this embodiment, a residual gas discharge section is formed in the core mold at a position opposite to the pin gate provided in the cavity mold, which discharges residual gas in the cavity to the outside of the mold when molten resin is filled into the cavity. As a result, a large amount of residual gas that is temporarily pushed out from inside the sprue and runner through the gate opening by the molten resin is discharged from the residual gas discharge section provided in close proximity to the pin gate.

[0017] Therefore, compared to a design without such residual gas discharge, the large amount of residual gas temporarily pushed out from within the sprue and runner through the gate opening is added to the residual gas in the cavity, increasing the pressure and mitigating the obstruction of molten resin flow within the cavity. This allows for rapid filling of the cavity with molten resin even at relatively low injection pressures, improving the filling performance of thin-walled molding.

[0018] Furthermore, because filling can be performed at a relatively low injection pressure, uneven distortion within the resin caused by high pressure is suppressed. As a result, the solidified resin can be easily and smoothly cut at the boundary between the gate opening and the molded product, further suppressing the generation of burrs and other defects at the gate marks on the molded product.

[0019] The third embodiment of the injection molding die is an injection molding die of the first embodiment in which, in the core mold, a molten metal reservoir is formed in the portion facing the pin gate, and the opening diameter of the pin gate is greater than the maximum thickness of the cavity at the position of the molten metal reservoir.

[0020] In the third embodiment of the injection molding die, a molten resin reservoir, which is a concave depression along the spherical surface, is formed in the core mold portion opposite the pin gate. As a result, the wall thickness of the cavity directly below the pin gate increases by the depth of the molten resin reservoir, widening the flow path. Furthermore, the molten resin injected at high speed from the pin gate hits the depression along the spherical surface of the molten resin reservoir and bounces off at an angle, causing the molten resin to be deflected laterally along the depression along the spherical surface. This results in a smoother flow of molten resin compared to when there is no molten resin reservoir. Moreover, the homogeneity of the resin in this area is improved, irregular irregularities on the fracture surface that occur when the solidified resin is cut at the gate opening are suppressed, and even if a depression occurs in the gate mark of the molded product due to fracture, the wall thickness of the gate mark area is maintained, and the strength of the molded product can be preserved.

[0021] The resin molded product of the fourth embodiment has a gate mark on one surface of the molded product, and the diameter of the gate mark is greater than the thickness of the resin at the location of the gate mark.

[0022] The resin molded product of the fourth embodiment has a gate mark. Generally, a resin molded product having a gate mark is formed by injecting molten resin through a gate into a cavity formed between a core mold and a cavity mold.

[0023] Furthermore, in the resin molded product of the fourth embodiment, the diameter of the gate mark is greater than the thickness of the resin. In other words, the opening diameter of the gate in the mold is greater than the thickness of the cavity. When molten resin is injected into the cavity through the gate, the molten resin is cooled and solidified by the core mold and the cavity mold. In this case, the gate portion with a large opening diameter cools more slowly than the cavity portion with a thin thickness, and therefore the difference in solidification rates between the two portions becomes large.

[0024] Therefore, when the cavity mold and core mold are opened, the resin is more easily cut at the pin gate position, suppressing the formation of protruding burrs at the gate mark of the molded product. In other words, because the diameter of the gate mark is greater than the thickness of the resin at the gate mark position, a relatively flat gate mark is formed, suppressing the generation of burrs and other protrusions at the gate position of the molded product.

[0025] According to the resin molded product of the fifth aspect, in the resin molded product of the fourth aspect, on the other surface of the molded product facing the gate mark, there is a residual gas discharge portion mark.

[0026] The residual gas discharge portion mark refers to a trace of the residual gas discharge portion provided in the core mold in the second aspect that can be seen on the surface of the resin molded product. That is, it refers to a portion where the boundary between the residual gas discharge portion and the other core mold portions can be identified on the resin molded product by minute burrs formed by the molten resin that has leaked along the boundary surface of the residual gas discharge portion in the core mold, or by color tone changes inside and outside the boundary.

[0027] Similar to the resin molded product of the fourth aspect, the thickness of the resin in the resin molded product of the fifth aspect is smaller than the diameter of the gate mark. That is, the thickness of the cavity in the mold is smaller than the opening diameter of the gate. When the thickness of the cavity is thin like this, when injecting molten resin into the cavity, a higher injection pressure is required compared to the case where the thickness of the cavity is thick.

[0028] Therefore, in the resin molded product of the fifth aspect, a residual gas discharge portion mark is formed on the other surface facing the gate mark. That is, at a position in the core mold facing the gate, a residual gas discharge portion for discharging residual gas from the cavity is formed. For this reason, a part of the large amount of residual gas that is temporarily extruded from the sprue and the runner through the gate opening by the molten resin is discharged from this nearest residual gas discharge portion.

[0029] As a result, the degree to which the residual gas hinders the flow of the molten resin in the cavity is suppressed, and the molten resin can be quickly filled into the cavity. As a result, the filling property of thin-wall molding can be improved. In addition, since it can be filled with a relatively low injection pressure, non-uniform strain inside the resin caused by high pressure is suppressed. Thereby, the resin is more easily and smoothly cut at the boundary between the gate opening and the molded product, and the generation of burrs and the like in the gate mark of the molded product is further suppressed.

Advantages of the Invention

[0030] According to the present invention, it is possible to suppress the generation of burrs exceeding the acceptable range at gate marks on molded products. [Brief explanation of the drawing]

[0031] [Figure 1] This is a cross-sectional view showing an injection molding die according to this embodiment. [Figure 2] (A) is a cross-sectional view showing an example of an injection-molded product according to this embodiment, (B) is a cross-sectional view showing another example, and (C) is a cross-sectional view showing yet another example. [Figure 3] This is a cross-sectional view showing an injection-molded product relating to a comparative example. [Figure 4] This is a cross-sectional view showing the state in which resin is being injected into the injection molding die according to this embodiment. [Modes for carrying out the invention]

[0032] Embodiments of the present invention are described below. In the following drawings, identical and similar parts are denoted by the same or similar reference numerals. However, the drawings are schematic, and the relationship between thickness and planar dimensions, the ratio of the thickness of each device and component, etc., may differ from reality. Therefore, specific thicknesses and planar dimensions should be determined by referring to the following explanation. Furthermore, there are parts where the relationships and ratios of dimensions differ between drawings.

[0033] <Injection mold> As shown in Figure 1, the injection molding die 10 according to this embodiment has a cavity die 12 and a core die 14. Note that only a portion of the injection molding die 10 is shown in Figure 1.

[0034] In this invention, the injection molding die is divided into two main parts so that molten resin can be filled into the cavity, which is the molding space inside the die, and the molded product can be removed from the cavity after it has cooled and solidified. Of these die parts, the die part that is connected to the molten resin injection nozzle of the injection molding machine and has a gate, which is the outlet for discharging the molten resin into the cavity, is called the "cavity die". On the other hand, of the two divided die parts, the die part that is opposite the "cavity die" is called the "core die".

[0035] In the injection molding die 10 according to this embodiment, a cavity mold 12 and a core mold 14 are superimposed, and a resin molded product is formed by injecting molten resin into the cavity 13 (molding space) formed between the cavity mold 12 and the core mold 14. The injection molding die 10 also has a pin gate 16 and a residual gas discharge section 18.

[0036] In this invention, "residual gas" refers to the gas present in the cavity during the process of filling the cavity with molten resin, and consists of air that is present from the beginning, air that is pushed out from sprues and runners when the injection of molten resin begins, and volatile components of the resin.

[0037] (Cavity) The cavity 13 according to this embodiment comprises a molten metal reservoir 13A and a planar space 13B. The molten metal reservoir 13A is the part that forms the convex portion 30A of the resin molded product 30 (see Figure 2). The molten metal reservoir 13A is a concave depression (dimple) along the spherical surface formed in the core mold 14 in the portion facing the pin gate 16. In this invention, the diameter of the spherical surface along which the molten metal reservoir follows is not particularly limited, but in this embodiment, the diameter of the spherical surface along which the molten metal reservoir 13A follows is set to a radius of approximately 5 mm.

[0038] Furthermore, in this invention, the depth of the water reservoir is not particularly limited, but in this embodiment, the depth H1 of the water reservoir 13A is set to approximately 0.7 mm. Also, the depth H1 is the depth in the direction perpendicular to the surface forming the planar space portion 13B in the core mold 14, and is the depth of the center (bottom) of the water reservoir 13A, and is the deepest depth.

[0039] The planar space portion 13B according to this embodiment is a portion formed around the convex portion 30A of the resin molded product 30 (see Figure 2). In the present invention, the thickness of the planar space portion is not particularly limited, but in this embodiment, the thickness H2 of the planar space portion 13B is set to about 0.2 mm. The thickness H2 is the thickness in the direction perpendicular to the surface forming the planar space portion 13B, and is the distance between the surface of the cavity mold 12 and the surface of the core mold 14.

[0040] The maximum thickness of the cavity 13 in the portion where the molten metal pool 13A is formed is thickness H3. Thickness H3 is the thickness of the cavity 13 at the position of the pin gate 16, and is also the sum of depth H1 and depth H2 (H3 = H1 + H2).

[0041] (gate) In this embodiment, the pin gate 16 injects molten resin into the molten pool 13A of the cavity 13. The pin gate 16 comprises a sprue 16A through which the molten resin injected into the cavity 13 flows, and a gate land 16B. The gate land 16B is provided at the tip of the pin gate 16, i.e., the end on the cavity 13 side, and is a tapered portion that decreases in diameter toward the cavity 13 side. The tip of the gate land 16B, i.e., the end on the cavity 13 side, is called the gate opening 16C, and the opening diameter φ1 of the gate opening 16C is greater than the maximum thickness H3 of the cavity 13 at the position of the molten pool 13A (φ1 > H3).

[0042] (Residual gas discharge section) In this embodiment, the residual gas discharge section 18 is configured to include a gas vent hole 18A and a plug member 18B. The residual gas discharge section 18 is formed in the core mold 14 at a position opposite the pin gate 16 of the cavity mold 12, and discharges residual gas from within the cavity 13.

[0043] Furthermore, in this invention, the location where the residual gas discharge section is formed is not limited to this. For example, the residual gas discharge section can be provided at a different location in the core type, or it can be provided in the cavity type. Also, the residual gas discharge section may be formed on the parting surface. Moreover, in this invention, the installation of the residual gas discharge section is an option, not a requirement.

[0044] (Gas vent hole) The gas vent hole 18A according to this embodiment reaches the center (deepest part) of the molten metal reservoir 13A from outside the mold. In other words, the gas vent hole 18A opens into the center of the molten metal reservoir 13A.

[0045] However, in the present invention, the opening position of the gas vent hole is not limited to the center of the molten metal pool, but can be placed at any position between the center of the molten metal pool and the outer edge (boundary with the planar space). The gas vent hole 18A in this embodiment is provided to discharge residual gas remaining in the vicinity of the center of the molten metal pool 13A. Specifically, the residual gas is air remaining in the vicinity of the center of the molten metal pool 13A, gases such as resin volatile components, or a mixture of these gases.

[0046] In this embodiment, the opening of the gas vent hole 18A facing the resin molded product 30 (see Figure 2) is circular in shape with a diameter of approximately 2.0 mm. In this invention, the dimensions and shape of the opening can be changed as appropriate. The shape of the gas vent hole according to this invention can be set to any geometric shape, such as a polygon or an ellipse. Therefore, the shape of the residual gas discharge mark formed on the resin molded product also changes according to the shape of the gas vent hole.

[0047] (Stopper component) The plug member 18B according to this embodiment is provided in a state in which it is detachably inserted into the gas vent hole 18A. The plug member 18B is a cylindrical material that is in close contact with the inner circumference of the gas vent hole 18A. The plug member 18B has a shaft portion and a head portion (flange portion) that is larger in diameter than the shaft portion. The head portion is not shown in the figure, but it is designed to be detachably fixed to the core mold 14 by screws or the like. The outer diameter of the shaft portion of the cylindrical material of the plug member 18B is approximately equal to the inner diameter of the gas vent hole 18A. In this invention, the shape of the plug member is not limited to a cylindrical shape, and may be other shapes such as a rectangular prism depending on the shape of the gas vent hole.

[0048] By removing the stopper member 18B according to this embodiment from the gas vent hole 18A, the stopper member 18B and the gas vent hole 18A can be easily cleaned when not being molded.

[0049] (Gas flow path) A gas channel 20 is formed on the outer circumferential surface of the cylindrical plug member 18B according to this embodiment, having an opening diameter that prevents molten resin from passing through but allows residual gas to pass through. The gas channel 20 is a narrow gas channel that leads from inside the cavity 13 to the outside of the mold, through which residual gas can pass but molten resin has difficulty passing.

[0050] The opening diameter of the gas passage 20 according to this embodiment is approximately 2 / 100 mm. However, the opening diameter of the gas passage is not limited to this in the present invention. For example, when designing the mold, the type of resin material used for molding, the temperature of the molten resin, molding conditions such as injection pressure, and the length and flexibility of the gas passage can be considered, and an appropriate opening diameter can be arbitrarily determined for each element.

[0051] The gas passage 20 illustrated in Figure 1 is formed between the inner surface of the gas vent hole 18A and the outer surface of the shaft portion of the stopper member 18B, with the outer surface of the stopper member 18B and the inner surface of the gas vent hole 18A in close contact. The gas passage 20 is formed by a gap 18B1 formed on the outer circumferential surface of the stopper member 18B along the axial direction of the stopper member 18B.

[0052] In this embodiment, the gap 18B1 is formed by cutting out the outer circumferential surface of the plug member 18B with a plane parallel to the axial direction of the plug member 18B. In this invention, the gap that serves as the gas passage may also be formed by creating a groove along the axial direction of the plug member on the outer circumferential surface of the plug member. Furthermore, the number of gaps that serve as gas passages is arbitrary, and they may merge or branch along the way. In addition, the cross-sectional dimensions of the gaps may be arbitrarily made larger in other downstream portions, as long as the opening diameter in the portion in contact with the cavity is such that molten resin cannot pass through but residual gas can pass through.

[0053] <Resin molded products> By using the injection molding die 10 according to this embodiment, a resin molded product 30 (hereinafter also simply referred to as molded product 30) shown in Figure 2(A) can be molded. The molded product 30 comprises a convex portion 30A and a flat portion 30B formed around the convex portion 30A.

[0054] The convex portion 30A is a thick-walled portion formed by the resin filling the molten metal reservoir 13A in the injection molding die 10. The flat portion 30B is a thin-walled portion formed by the resin filling the flat space portion 13B in the injection molding die 10.

[0055] In this invention, "thin-walled" refers to a wall thickness in which the thinness of the cavity results in high flow resistance of the molten resin, requiring a high injection pressure for the molten resin, which in turn increases the load on the molding machine, increases the flow velocity of the molten resin, and consequently causes distortion in the molded product. It does not mean a wall thickness below a specific thickness.

[0056] In the molded product 30 according to this embodiment, a gate mark 32 and a residual gas discharge mark 34 are formed at the location of the protrusion 30A. The gate mark 32 is formed on the surface of the molded product 30 that contacts the cavity mold 12 during molding, and is a mark having a shape corresponding to the opening shape of the pin gate 16 (gate land 16B). On the other hand, the residual gas discharge mark 34 is formed on the surface of the molded product 30 that contacts the core mold 14 during molding, and is a mark having a shape corresponding to the cavity-side end shape of the residual gas discharge section 18.

[0057] The diameter φ1A of the gate mark 32 is approximately equal to the opening diameter φ1 of the gate land 16B (see Figure 1), and is greater than the resin thickness (wall thickness) H3A at the location where the gate mark 32 is formed. Furthermore, this thickness H3A is approximately equal to the maximum thickness H3 of the cavity 13 at the location of the molten metal pool 13A (see Figure 1).

[0058] In the example shown in Figure 2(A), the gate mark 32 is formed almost flush with the surrounding area. On the other hand, in the example shown in Figure 2(B), the gate mark 32 is formed recessed from the surrounding area. Furthermore, in the example shown in Figure 2(C), the gate mark 32 is formed raised from the surrounding area.

[0059] As shown in these examples, in the present invention, the gate mark may be substantially flush with the surrounding portion, recessed, or raised. In each of these cases, the gate mark does not necessarily have to be a trace that can be seen with the naked eye or felt by touch. The gate mark 32 may be formed by irregularities that can be perceived, for example, when magnified to about 100 times or more with an optical microscope, or to about 1000 times or more. The same applies to residual gas discharge marks. As mentioned above, just as a residual gas discharge section is not essential for the injection molding die of the present invention, a residual gas discharge mark is not essential for the molded product.

[0060] <Mechanism and Effects> According to the injection molding die 10 of this embodiment, as shown in Figure 1, the opening diameter φ1 of the pin gate 16 formed in the cavity mold 12, that is, the opening diameter φ1 of the gate opening 16C, is greater than the thickness H3 at the position of the pin gate 16 in the cavity 13 formed between the core mold 14 and the cavity mold 12.

[0061] Generally, as shown in Figure 4, for example, when molten resin is injected into a cavity through a pin gate, the molten resin is cooled and solidified by the core mold and cavity mold. In areas with thinner walls, the cooling rate of the molten resin is faster than in areas with thicker walls due to the difference in heat capacity, and therefore the solidification rate is also faster.

[0062] In this embodiment, the opening diameter φ1 of the pin gate 16 is made larger than the thickness H3 of the cavity 13 at the position of the pin gate 16. This increases the amount of molten resin inside the pin gate 16, and thus increases the heat capacity. As a result, after the injection of the molten resin is completed, when the molten resin upstream of the gate opening 16C is cooled and solidified by the surrounding cavity mold 12, the solidification speed is suppressed and becomes relatively slow due to its proximity to the heat source.

[0063] In this way, by controlling the difference in solidification speed between the molten resin inside the pin gate 16 and the molten resin inside the cavity 13 at the location of the pin gate 16, and by increasing the difference in thermal shrinkage, distortion occurs in a layered manner at the boundary between the solidified resin gate opening 16C and the molded product.

[0064] Therefore, in this embodiment, when the cavity mold 12 and the core mold 14 are opened and a tensile force is applied between the solidified resin in the pin gate 16 and the solidified resin in the cavity 13 at the pin gate 16 position, stress concentrates in the constricted portion of the boundary between the gate opening 16C and the molded product, and a crack, which is a partial fracture, first occurs on the outer circumference of the constricted portion. Then, the fracture progresses toward the center and finally separates at this point. As a result of this fracture progression being guided along the boundary between the gate opening 16C and the molded product where a weakened layer is formed due to concentrated strain, the solidified resin becomes easier to cut relatively smoothly. As a result, as shown in Figures 2(A) to (C), the generation of burrs and the like at the gate mark 32 on the molded product 30 is suppressed.

[0065] Furthermore, generally speaking, when the cavity thickness is thin according to the shape specifications of a resin molded product, a higher injection pressure is required when injecting molten resin into the cavity compared to when the cavity thickness is thicker. This can easily lead to increased load on the molding machine, increased flow rate of molten resin, and resulting distortion of the molded product.

[0066] Therefore, in the injection molding die 10 according to this embodiment, a residual gas discharge section 18 is provided in the core mold 14 at a position opposite to the pin gate 16 provided in the cavity mold 12, for discharging residual gas from within the cavity 13. This residual gas discharge section 18 has a gas passage 20, which is a narrow gas passage that leads from within the cavity 13 to the outside of the mold, through which residual gas can pass but molten resin cannot. As a result, a large amount of residual gas that is temporarily pushed out from within the sprue 16A (and within the runner if there is a runner) through the gate opening 16C by the molten resin is discharged from the gas passage 20 provided in the residual gas discharge section 18 immediately adjacent to the pin gate 16.

[0067] With this embodiment, compared to a configuration without such a residual gas discharge section 18, the amount of residual gas temporarily pushed out from inside the sprue 16A through the gate opening 16C is added to the residual gas in the cavity 13, increasing the pressure and mitigating the degree to which the flow of molten resin in the cavity 13 is hindered. As a result, molten resin can be quickly filled into the cavity 13 even at relatively low injection pressures, that is, the filling performance of thin-wall molding can be improved.

[0068] Furthermore, by providing a residual gas discharge section 18, filling can be performed at a relatively low injection pressure, thereby suppressing uneven distortion within the resin caused by high pressure. As a result, the resin can be easily and smoothly cut at the boundary between the gate opening 16C and the molded product 30 (see Figure 2), further suppressing the generation of burrs and other defects at the gate mark 32 of the molded product 30.

[0069] Furthermore, in the injection molding die 10 according to this embodiment, a molten metal reservoir 13A, which is a concave depression along the spherical surface, is formed in the portion of the core mold 14 facing the pin gate 16. As a result, the wall thickness of the cavity 13 directly below the pin gate 16 becomes thicker by the depth H1 of the molten metal reservoir 13A, and the flow path is widened.

[0070] Furthermore, the molten resin injected at high speed from the pin gate 16 does not bounce vertically off the wall surface of the core mold 14, and the reflection is deflected laterally by the slope of the depression along the spherical surface, resulting in a smoother flow of the molten resin compared to when there is no molten resin reservoir 13A.

[0071] As a result, the homogeneity of the solidified resin in the molten resin pool 13A is improved, and when the solidified resin is cut at the gate opening 16C, the occurrence of irregularities exceeding the allowable range in the gate mark 32 is suppressed. Furthermore, as shown in Figure 2(B), even if a dent occurs in the gate mark 32 of the molded product 30 due to fracture, the wall thickness of the gate mark 32 is maintained, and the strength of the molded product 30 can be preserved.

[0072] Furthermore, the resin molded product 30 according to this embodiment has a gate mark 32, as shown in Figure 2. The resin molded product 30 having a gate mark 32 is molded by injecting molten resin through a pin gate 16 into a cavity 13 formed between a core mold 14 and a cavity mold 12, as shown in Figure 1.

[0073] Furthermore, in this resin molded product 30, the diameter φ1A of the gate mark 32 is greater than the resin thickness H3A at the location where the gate mark 32 is formed. In other words, the opening diameter φ1 of the gate opening 16C in the mold 10 shown in Figure 1 is greater than the thickness H3 of the cavity 13.

[0074] Generally, as shown in Figure 4, for example, when molten resin is injected into a cavity through a pin gate, the molten resin is cooled and hardened by the core mold and cavity mold. In the molding of the resin molded product 30 according to this embodiment, the molten resin in the gate opening 16C portion, which has a large opening diameter, cools more slowly than the molten resin in the cavity 13 portion, which has a thinner thickness, and therefore the difference in hardening speed between the two portions becomes large.

[0075] Therefore, when the cavity mold 12 and the core mold 14 are demolded, the resin is easily cut at the gate opening 16C of the pin gate 16, and as shown in Figure 2, the protruding burrs that occur at the gate mark 32 of the molded product 30 are suppressed. In other words, because the diameter φ1A of the gate mark 32 is greater than the thickness H3A of the resin at the location of the gate mark 32, a relatively flat gate mark 32 is formed as shown in Figures 2(A), (B), or (C), compared to the gate mark 320A in the comparative example shown by the dashed line in Figure 2(C) or the comparative example shown in Figure 3, and the generation of burrs and the like that protruding at the pin gate 16 position of the molded product 30 is suppressed.

[0076] In Figure 2(C), the height of the protruding burr in the gate mark 320A is approximately equal to the diameter φ1A of the gate mark 320A. However, generally, the height of the burr is irregular, sometimes being larger than the diameter of the gate mark, and sometimes smaller, making it difficult to control. On the other hand, in the resin molded product of the present invention, even when the gate mark is formed to protrude from the surrounding area, the height of the burr is suppressed to be lower than the diameter of the gate mark, as shown in Figure 2(C), for example, the gate mark 32.

[0077] Figure 3 shows a molded product 300 relating to a comparative example. The molded product 300 is an injection-molded product with a relatively thick solidified resin thickness (approximately cavity thickness) H100. A gate mark 320 is formed on the molded product 300. The gate mark 320 is formed on the surface of the molded product 300 that contacts the cavity mold (not shown) during molding, and is a mark with a diameter of φ100, corresponding to the shape of the opening of the pin gate (not shown) provided in the cavity mold.

[0078] The diameter φ100 of the gate mark 320 according to this comparative example is an example where, unlike the present invention, it is smaller than the thickness H100 of the molded product 300 (φ100 < H100). That is, the opening diameter of the gate opening (not shown) in the mold (not shown) for molding this molded product 300 is smaller than the thickness of the cavity.

[0079] When molding the molded product 300 according to this comparative example, the molten resin injected into the cavity is cooled and cured by the core mold (not shown) and the cavity mold, similar to the case of the present invention. However, unlike the case of the present invention, the molten resin in the gate opening portion with a relatively small opening diameter has a relatively small difference in the cooling rate compared to the molten resin in the cavity portion with a relatively large thickness. For this reason, a fragile layer where distortion is concentrated is not sufficiently formed at the position of the gate opening. Therefore, when the cavity mold and the core mold are separated, the cutting of the solidified resin does not proceed smoothly at the position of the gate opening, and as shown in FIG. 3, relatively large protruding burrs are likely to occur on the gate mark 320 of the molded product 300. Generally, when forcibly broken by tensile force in this way, the shape of the unevenness generated on the fracture surface is dominated by chance and cannot be predicted. For example, the height of the gate mark may be about the diameter of the gate mark or more. (H100 ≠ φ100)

[0080] Also, in the resin molded product 30 according to the present embodiment, the thickness H3A of the solidified resin is smaller than the diameter φ1A of the gate mark 32. That is, the thickness H3 of the cavity 13 in the mold 10 shown in FIG. 1 is smaller than the opening diameter φ1 of the gate opening 16C. Generally, when injecting resin into the cavity, when the thickness of the cavity is thin, a higher injection pressure is required compared to when the thickness of the cavity is thick.

[0081] In the resin molded product 30 according to this embodiment, a residual gas discharge mark 34 is formed on the other surface opposite to the gate mark 32. That is, in the core mold 14 shown in Figure 1, a residual gas discharge section 18 is formed at a position opposite to the pin gate 16 of the cavity mold 12 to discharge gas from the cavity 13. Therefore, a portion of the large amount of residual gas that is temporarily pushed out from inside the sprue 16A through the gate opening 16C by the molten resin is discharged from the gas passage 20 provided in this immediate residual gas discharge section 18.

[0082] This reduces the degree to which residual gas hinders the flow of molten resin within the cavity 13, allowing the molten resin to be quickly filled into the cavity 13 and improving the filling performance of thin-walled molding. Furthermore, since filling can be done at a relatively low injection pressure, uneven distortion within the solidified resin caused by high pressure is suppressed. As a result, the resin can be easily and smoothly cut at the boundary between the gate opening 16C and the molded product 30, further suppressing the generation of burrs and other defects at the gate mark 32 of the molded product 30.

[0083] <Other Embodiments> In the above embodiment, as shown in Figure 1, the cavity 13 comprises a molten metal reservoir 13A and a planar space 13B, but the embodiments of the present invention are not limited to this. For example, the cavity does not have to have a molten metal reservoir. In this case, it is sufficient that the opening diameter of the pin gate formed in the cavity type, i.e., the opening diameter of the gate opening, is larger than the thickness of the planar space.

[0084] Furthermore, even in embodiments without a water reservoir, a residual gas discharge section can be formed at a position opposite to the pin gate provided in the cavity type to discharge residual gas from within the cavity.

[0085] Although the present invention has been described by the embodiments disclosed above, the descriptions and drawings that constitute part of this disclosure should not be understood as limiting the present invention. The present invention includes embodiments that appropriately combine each of the embodiments described above, as well as various embodiments not described above, and the technical scope of the present invention is defined solely by the inventive features of the claims that are reasonable from the above description. [Explanation of symbols]

[0086] 10 Injection mold 12 Cavity Type 13 Cavity 13A Hot water pool 14-core type 16-pin gate 18 Residual hot water gas discharge section 30 Molded products 32 Gate marks 34 Traces of residual gas discharge

Claims

1. An injection molding die having a core mold and a cavity mold, wherein the core mold and the cavity mold are superimposed and molten resin is injected into the cavity formed between the core mold and the cavity mold to form a resin molded product, The cavity mold is formed and includes a pin gate for injecting molten resin into the cavity, In the core mold, a molten metal reservoir, which is a concave depression along the spherical surface, is formed in the portion facing the pin gate. The opening diameter of the pin gate is greater than the maximum thickness of the cavity at the location of the molten metal reservoir. Mold for injection molding.

2. The bottom surface of the aforementioned molten resin reservoir is provided with a residual gas discharge section that discharges residual gas from within the cavity to the outside of the injection molding die when molten resin is filled into the cavity. The injection molding die according to claim 1.

3. The inner diameter of the aforementioned hot water reservoir is wider than the opening diameter of the aforementioned pin gate. The injection molding die according to claim 1.

4. It comprises a protrusion projecting from one side of the surface and a flat portion formed around the protrusion, The other surface of the aforementioned protrusion has a gate mark, The diameter of the gate mark is greater than the thickness of the resin forming the protrusion at the location of the gate mark, and the surface of the flat portion and the surface from which the protrusion protrudes form an obtuse angle. Resin molded product.

5. In the aforementioned protrusion, the surface facing the gate mark has a residual gas discharge mark. The resin molded article according to claim 4.

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